U.S. patent number 5,833,787 [Application Number 08/542,168] was granted by the patent office on 1998-11-10 for process for making a nonwoven web derived from lactic acid, web produced thereby, and apparatus therefor.
This patent grant is currently assigned to Fiberweb Sodoca Sarl. Invention is credited to Philippe Ehret, Philippe Guipouy, Kimmo Lahtenkorva.
United States Patent |
5,833,787 |
Ehret , et al. |
November 10, 1998 |
Process for making a nonwoven web derived from lactic acid, web
produced thereby, and apparatus therefor
Abstract
The invention relates to a process for the manufacture of a
nonwoven web using filaments of melted polymers, of the type
including the steps of spinning the polymer or polymers, of
cooling, drawing and laying down fibers on a belt and of bonding
said fibers by calendering in order to form said nonwoven web (15),
which process furthermore includes a treatment (13, 14) of
setting/adjusting the degree of crystallinity of and the internal
tension in the fibers making up the nonwoven web. The invention
also relates to the nonwovens obtained by the process and to the
installations for implementing it.
Inventors: |
Ehret; Philippe (Fortschwihr,
FR), Guipouy; Philippe (Guebwiller, FR),
Lahtenkorva; Kimmo (Kayersberg, FR) |
Assignee: |
Fiberweb Sodoca Sarl (Biesheim,
FR)
|
Family
ID: |
9467900 |
Appl.
No.: |
08/542,168 |
Filed: |
October 12, 1995 |
Foreign Application Priority Data
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Oct 12, 1994 [FR] |
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94 12332 |
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Current U.S.
Class: |
156/167; 156/229;
264/210.8; 264/290.2; 264/290.5 |
Current CPC
Class: |
D04H
1/556 (20130101); D04H 1/435 (20130101); D04H
3/14 (20130101); D04H 3/16 (20130101); D04H
1/54 (20130101) |
Current International
Class: |
D04H
1/54 (20060101); D04H 1/42 (20060101); D04H
001/42 (); D04H 003/16 () |
Field of
Search: |
;264/290.2,210.5,210.8,290.5 ;156/164,167,229 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0514137 |
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Nov 1992 |
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EP |
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0569154 |
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Nov 1993 |
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EP |
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0637641 |
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Feb 1995 |
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EP |
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2709500 |
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Mar 1995 |
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FR |
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5134425 |
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Jun 1993 |
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JP |
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1213441 |
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Nov 1970 |
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GB |
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Primary Examiner: Ball; Michael W.
Assistant Examiner: Yao; Sam Chuan
Attorney, Agent or Firm: Weiser and Associates P.C.
Claims
We claim:
1. A process for the manufacture of a nonwoven web using fibers of
one or more melted polymers, consisting of lactic acid or a
derivative thereof, and wherein the process comprises the steps of
spinning the melted polymer to form the fibers, cooling, drawing
and laying down the fibers on a belt, bonding said fibers by
calendaring to form the web, and setting/adjusting the degree of
crystallinity of and the internal tension in the fibers of the
nonwoven web, the setting/adjusting consisting essentially of
biaxial setting after the calendaring, then low temperature heating
the web under biaxial tension, followed by cooling.
2. The process of claim 1, wherein the heating is oven heating for
10 to 60 s at a temperature varying from 80.degree. C. to
150.degree. C.
3. The process of claim 1, wherein the heating is heating for a few
seconds by infrared radiation at a temperature varying from
80.degree. C. to 150.degree. C.
4. The process of claim 1 wherein the polymer is a polymer of
L-lactic acid or D-lactic acid.
5. The process of claim 4 wherein the polymer is a polymer of
L-lactic acid and D-lactic acid.
6. The process of claim 1 wherein the degree of crystallinity is
increased.
7. The process of claim 1 wherein the internal tension in the
fibers is relaxed.
8. The process of claim 1 wherein the degree of crystallinity is
increased and the internal tension in the fibers is relaxed.
9. An apparatus for implementing the process of claim 1 for the
manufacture of a non-woven web using polymers, of the type
including means of spinning the polymer or polymers, of cooling,
drawing and laying down fibers on a belt and of bonding said fibers
by calendaring in order to form a web, which apparatus furthermore
includes treatment means for setting/adjusting the degree of
crystallinity of and the internal tension in fibers making up the
web, wherein the setting/adjusting treatment means comprises means
for biaxial-setting the web and means for low-temperature heating
of the web under biaxial tension.
10. The apparatus of claim 9, wherein the setting/adjusting
treatment means consist of biaxial-setting means and of heating
means selected from the group: oven, and infrared radiation.
11. The apparatus of claim 9, wherein the setting/adjusting
treatment means further comprises cooling means for cooling the web
following the means for low temperature heating.
Description
The invention relates to a process for manufacturing a nonwoven web
based on polylactides.
BACKGROUND OF THE INVENTION
Nonwovens are often manufactured by a manufacturing process called
spin bonding (SB) using fibers of nonbiodegradable polymers since
the use of biodegradable compounds, such as lactic acids, leads to
nonwovens whose stability and mechanical properties are currently
difficult to control.
Today, throughout the world, sites for discharging solid waste are
becoming rapidly saturated. This waste comprises a large amount of
nonwoven products from diapers (for babies and adults), products
for feminine hygiene (sanitary napkins), disposable protective
clothing, nonwoven products used in agriculture and many other
products.
Recently there has been a tendency to promote a reduction in the
flow of waste to discharge sites by opting for composting. However,
all the nonwoven products mentioned above are conventionally
manufactured from polyolefins, PE (polyethylene), PP
(polypropylene), and from their blends or from other polymers which
do not allow composting. The solution lies in producing
biodegradable polymers, the degradation of which is carried out by
the municipalities in their solid-waste composting systems.
Several biodegradable polymers exist on the market, for example
copolymers based on polyhydroxybutyrate/valerate (PHB/V). (Zeneca
Bio Products: BIOPOL), polycaprolactones (PCL), (Union Carbide:
TONE, Interox Chemicals: CAPA), several polymers based on starch or
starch derivatives, (Warner-Lambert: NOVON), polymers based on
polyglycolic acid (PGA), polymers based on polylactides (PLA),
(Boehringer Ingelheim: RESOMER) and other biodegradable
polyesters.
The subject matter of European Patent Application No. 93303009.9 of
Apr. 19, 1993, the inventor of which is Showa Shenko K. K., is
biodegradable aliphatic polyesters used as a material for
disposable diapers (also nonwoven parts).
Polylactide (called PLA) or its derivatives (L and D type or
copolymers) is potentially one of the most degradable polymers
because it has good mechanical properties, it is totally
degradable, the degradable products are natural materials, the
degradation time can be varied, the raw material comes from
renewable sources such as beet sugar or whey and it can be
incinerated with no problem. It may be extruded in the form of a
film (European Patent Application No. 92304269.1 of May 12, 1992,
Mitsui Toatsu Chemicals, Inc.) or in the form of a bulk product and
it may be injection molded. Adding a heat stabilizer allows it to
be recycled and, finally, it may be melted and extruded, and
consequently it is suitable for producing nonwovens intended for
hygiene applications, as is described in French Patent 9309649, of
Aug. 2, 1993, and European Patent 944700186, FIBERWEB SODOCA and
Japanese Patent Application 134425 of Jun. 4, 1993, MITSUI TOASTU
CHEMICALS Inc.
The properties of polymers derived from polylactides vary depending
on the type of polymer (L or D type), on the residual amount of
monomer (lactide) and, in the case of DL copolymers, on the ratio
of D units to L units.
The process most often used to manufacture nonwovens is the process
called "spin bonding", abbreviated to SB hereafter. In this
process, the polymer is melted and extruded by means of a
single-screw or twin-screw extruder and then conveyed to the
spinning pump or pumps which are usually gear pumps. Frequently, a
filter and a static mixer are placed before the pumps.
On leaving the pumps, the stream of molten polymer is conveyed
through the filter to the spinneret, which contains a series of
small holes (0.2 to 2.0 mm in diameter), usually of the order of
several thousands. The polymer is spun through the spinneret and
conveyed to the cooling and drawings sections. Cooling may be by
forced chilled air and the drawing is achieved by suction of air or
air forced through the drawing section.
The drawing section may consist of a wide slit or several smaller
slits or nozzles. In the drawing section, the fibers have a
decreasing diameter and adopt an oriented structure. The draw ratio
is generally 1.1 to 20 x. In the SB process, the linear density of
the fibers is of the order of 0.5 to 20 dtex.
The spinning section is followed by a laydown section where the
fibers are laid down randomly on a belt. The belt conveys the
fibers to the calendar. The weight/m.sup.2 may be adjusted by
varying the speed of the belt.
FIG. 1 shows diagrammatically an installation for implementing a
known SB process (for example the S-Tox process) consisting mainly
of: (1) a hopper, (2) an extruder, (2') a screw, (3') a spinneret,
(4) a belt, (5) a bonding calender, (6) a means for guiding the web
and adjusting the wind-up tension, (7) a winding means, (9) a unit
for cooling the fibers, (11) a drawing nozzle and (11') drawing
suction.
The spinning in the SB process generates fibers of PLA having a
highly oriented structure (high degree of drawing and rapid
cooling).
This means that the amorphous phase is well oriented and has a high
internal tension, and that the fibers have a tendency to shrink
when using temperatures above the T.sub.g (glass transition
temperature), (Ahamad Y. A. Khan et al., "Melt processing of
poly(lactide) resin into nonwovens", TANDEC, University of
Tennessee).
The crystallinity and the state of the amorphous phase have a
considerable effect on the properties of the web. If the
crystallinity is too high, the web becomes brittle and if the
amorphous phase is under internal tension (a high degree of
orientation), it will shrink at high temperatures.
Conventional bonding processes (for example calendering between a
smooth roll and a heated etched roll, with external control of the
pressure, so that the bonded surface area is from 7 to 25%) at
temperatures between 70.degree. C. and 100.degree. C. (depending on
the grade and the type of polymer) cannot be carried out because of
the shrinkage, and, at lower temperatures, the bonding is not
optimal. In addition, if satisfactory bonding is achieved at a low
temperature, the product is found to have stability problems. In a
very humid atmosphere, the web shrinks at a temperature below
40.degree. C.
PLA has a tendency to stick at temperatures of between 70.degree.
and 100.degree. C. It is difficult to remove PLA laid down on the
calendering rolls when this sticking is combined with simultaneous
shrinkage. Calendering at high temperatures (>100.degree. C.)
increases the crystallinity considerably (very slow cooling), which
leads to a lower elongation.
SUMMARY OF THE PREFERRED BODY OF THE INVENTION
The main object of the invention is to provide a process for the
manufacture of a spun-bonded nonwoven (called an SB) based on
polylactides, which is biodegradable and which has characteristics
identical to those of conventional nonwovens based on
polyolefins.
More particularly, the process according to the invention is
intended to improve the mechanical properties of the
polylactide-based nonwoven and to stabilize it in order to prevent
shrinkage caused by high temperatures.
For this purpose, the process according to the invention makes it
possible to set or adjust the degree of crystallinity and the
internal tension of the fiber making up the web of PLA-based
nonwoven.
A process according to the invention applies to the manufacture, by
spin bonding, of a nonwoven exclusively composed of one or more
polymers derived from lactic acid, such as polylactides, that is to
say all the filaments of which it is composed are made entirely of
a polymer derived from lactic acid, or of a blend of polymers
derived from lactic acid or of a copolymer derived from lactic
acid.
Preferably, the polymer derives from an L- or D-lactic acid.
Preferably, the blend of polymers is a blend of polymers derived
from L-acid and derived from D-acid.
Preferably, the filaments of the nonwoven are derived from L- and
D-lactic acids (copolymers).
More particularly, a process according to the invention includes a
treatment of setting/adjusting the degree of crystallinity of and
the internal tension in the fibers making up the nonwoven web.
According to a first variant, the setting/adjusting treatment
consists of biaxial setting after the calendering, and then
low-temperature heating followed by cooling, it being possible for
said heating to be performed by any suitable means, for example in
an oven or by infrared radiation.
According to a second variant, the setting/adjusting treatment
consists of rapid cooling immediately after high-temperature
calendering.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood with the aid of the
following description, given with reference to the following
appended figures:
FIG. 1: a diagram of an installation for implementing a
spin-bonding or SB process of the prior art;
FIG. 2: a diagram of a setting/adjusting treatment assembly
according to the invention, which can be combined with an
installation as shown in FIG. 1;
FIG. 3: a diagram of another setting/adjusting treatment assembly
according to the invention, which can be combined with an
installation as shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED BODY OF THE INVENTION
The novelty of the process according to the invention is that it
includes at least one treatment for setting or adjusting the degree
of crystallinity of and the internal tension in the fibers making
up the PLA-based nonwoven web.
This setting/adjusting step may be carried out in the following two
ways (which are not limiting):
1) After calendering in a calender (16) and setting at (12) at low
temperature (see FIG. 2), the bonded web (15) (having biaxial
tension) is subjected to a temperature control in heating means
(13) and then cooled in cooling means (14).
If the calendering is performed at low temperature (70.degree. C.)
and at a reasonably high pressure, the bonding is satisfactory, but
the level of elongations and strengths is low and the web has a
tendency to shrink later when subjected to higher temperatures.
In order to eliminate this tendency and to improve the mechanical
properties, the web is set biaxially after calendering and heated
in an oven for 10 to 60 seconds at a temperature varying from
80.degree. C. to 150.degree. C., or heated for a few seconds (0.5
to 10 s) by an IR generator at a temperature varying from
80.degree. C. to 150.degree. C. These treatments may be performed
in-line or as a post-treatment.
The temperature control according to one or other of the heating
(13) variants has the effect of relaxing the internal tension and
increasing the degree of crystallinity. As a result, a higher
elongation and a higher strength are found and the web no longer
shrinks.
The heating time and the temperature must be chosen precisely in
order to prevent embrittlement of the web as a result of too high a
temperature.
2) A web (17) is bonded at a high calendering temperature in a
calender (18) and immediately rapidly cooled by cooling means
(19).
Good mechanical properties, no sticking to the calender and a web
having properties which are stable at high temperatures may be
obtained by using very high calendering temperatures (from
100.degree. to 150.degree. C.) and by cooling the web immediately
after calendering by blowing air onto it. This treatment produces
very satisfactory bonding and a degree of crystallinity which is
not too high. The web has an elongation and a satisfactory
strength, and is stable at high temperatures. The ideal temperature
depends on the weight/m.sup.2 of the nonwoven, on the type of
polymer, on the line speed and on the properties required.
Elongations 10 times higher and a strength twice as high as the
usual values are obtained using this method.
PREFERRED EXAMPLES
The invention will be illustrated by the following nonlimiting
examples:
The nonwoven webs used in theses examples are manufactured under
the following conditions:
______________________________________ Process: S-Tex Raw material:
PLLA Average molecular weight: 130,000-140,000 Polydispersity: 1.9
Melting point: 160-165.degree. C. Extrusion temperature:
190.degree. C.-210.degree. C. Spinning chilled air: 0.3-1.0 m/s,
10-20.degree. C. drawing: 30-90 mm/Ce Belt speed: 15-30 m/s
Calendar temperature: 50-70.degree. C. (as high as possible without
causing the web to shrink)
______________________________________
EXAMPLE 1
______________________________________ Nonwoven web
______________________________________ Initial values
Weight/m.sup.2: 25 g/m.sup.2 Denier: 2.5 dtex MD strength: 20 N/5
cm MD elongation: 5% Heat treatment Method: Biaxiality set and
heated oven Temperature: 100.degree. C. Duration: 2 min Improvement
in the properties (%) MD strength: 100% MD elongation: 1000% (10
fold) Shrinkage at 100.degree. C. without setting: Nonexistent
______________________________________
EXAMPLE 2
______________________________________ Nonwoven web
______________________________________ Initial values
Weight/m.sup.2: 65 g/m.sup.2 Denier: 2.5 dtex MD strength: 80 N/5
cm MD elongation: 26% Heat treatment Method: Biaxiality set and
heated oven Temperature: 100.degree. C. Duration: 2 min Improvement
in the properties (%) MD strength: 20% MD elongation: 400%
Shrinkage at 100.degree. C. without setting: Nonexistent
______________________________________
EXAMPLE 3
______________________________________ Nonwoven web
______________________________________ Initial values
Weight/m.sup.2: 26 g/m.sup.2 Denier: 1.8 dtex MD strength: 27 N/5
cm MD elongation: 10% Heat treatment Method: Biaxiality set and
heated on the S-Tex line with an IR heater Temperature:
approximately 120.degree. C. (maximum) power, 9 kW) Duration: 2 s
Improvement in the properties (%) MD strength: 40% MD elongation:
400% (4 fold) Shrinkage at 100.degree. C. without setting: 4-6%
______________________________________
EXAMPLE 4
In this example, the same process parameters are used, except that
the calendering temperature is higher, from 120.degree. to
150.degree. C., and cooling occurs immediately after calendering,
which reduce the temperature of the web to 20.degree.-60.degree. C.
Efficient cooling after calendering prevents the web from
shrinking.
______________________________________ Nonwoven web
______________________________________ Initial values
Weight/m.sup.2: 60 g/m.sup.2 Denier: 2.5 dtex MD strength: 65 N/5
cm MD elongation: 30% Heat treatment Method: Hot calendaring and
immediate cooling with blown air at a temperature of 15-30.degree.
C. Temperature: 120-150.degree. C. Improvement in the properties
(%) (if calendering is carried out at the temperatures mentioned in
Examples 1 to 3). MD strength: 40% MD elongation: 50% Shrinkage at
100.degree. C. without setting: 5-10%
______________________________________
In order to implement the process according to the invention, an
apparatus is set up for manufacturing a nonwoven web using
polymers, of the type including means of spinning the polymer or
polymers, of cooling, drawing and laying down fibers on a belt and
of bonding said fibers by calendering in order to form a web (15,
17), which process furthermore includes means for setting/adjusting
the degree of crystallinity of and the internal tension in fibers
making up the web (15, 17).
More particularly, the setting/adjusting treatment means consist of
biaxial-setting means (15) and of heating means (13) taken from the
group: oven, infrared radiation, or consist of rapid cooling means
(19) located just after calendering means (18) heated to high
temperature.
* * * * *